Traditionally, most commercially available inkjet printers have a print engine which forms part of the overall structure and design of the printer. The body of the printer unit is typically constructed to accommodate the printhead and associated media delivery mechanisms, and these features are integral with the printer unit.
This is especially the case with inkjet printers that employ a printhead that traverses back and forth across the media as the media progresses through the printer unit in small iterations. Typically, the reciprocating printhead is mounted to the body of the printer unit such that it can traverse the width of the printer unit between a media input roller and a media output roller, with the media input and output rollers forming part of the structure of the printer unit. It may be possible to remove the printhead for replacement, however the other parts of the print engine, such as the media transport rollers, control circuitry and maintenance stations, are usually fixed within the printer. Replacement of these parts is not possible without replacement of the entire printer.
As well as being rather fixed in their design construction, printers employing reciprocating type printheads are relatively slow, particularly when performing print jobs of full colour and/or photo quality. This is due to the fact that the printhead must continually scan the stationary media to deposit the ink on the surface of the media and it may take a number of swathes of the printhead to deposit one line of the image.
Recently, ‘pagewidth’ printheads have been developed that extend the entire width of the print media. The printhead remains stationary as the media is transported past its array of nozzles. This increases print speeds as the printhead no longer needs to perform a number of swathes to deposit a line of an image. Instead, the printhead deposits the ink on the media as it moves past at high speeds. With these printheads, full colour 1600 dpi printing at speeds of around 60 pages per minute are possible. Such speeds were unattainable with conventional inkjet printers.
High print speeds require high precision and high speed paper movement, and as such, the entire print engine (printhead, paper handling mechanisms and control circuitry etc) must be configured accordingly to ensure high quality output.
Accordingly, there is a need to provide a print engine having a pagewidth printhead that can be readily employed within a printer body for consistent, high speed printing.
Unfortunately, individual nozzles on a printhead will malfunction through clogging, air bubbles in the ink, fabrication errors and so on. Obviously, this is detrimental to print quality. It is possible to combat this with dead nozzle compensation in the print engine controller (PEC) and nozzle redundancy (surplus nozzles) on the printhead. However, eventually too many nozzles will fail for these mechanisms to work, and the print quality is compromised. By providing the printhead in a replaceable printhead cartridge, the printhead can be replaced when the print quality deteriorates, rather than replacing the entire printer.
A pagewidth printhead needs to be precisely mounted relative to the paper path. To do this with a replaceable printhead cartridge would typically require a fairly involved cartridge replacement procedure and or a complex cartridge cradle in the printer. This has disadvantages for both the end user and the manufacturer.
One particular complication with a replaceable pagewidth printhead involves the number of power and data contacts that need to connect to the printers onboard PEC. Pagewidth printheads have far more nozzles than scanning printheads, so the number of power and data contacts is also much greater. The printer has corresponding contacts leading to the PEC. The connection between each individual pair of corresponding contacts needs to be such that the opposing contact pads are pressed against each other with a predetermined force. The specified force ensures that the electrical connection between the contact pads is maintained.
To initially connect the contacts requires that they be pushed together with a certain force. For a pagewidth printhead, the large number of contacts makes the force required to push all of them together simultaneously, relatively high (about 10 kg). This is inconvenient for users and puts a large and potentially damaging load on the structure of the printhead and the printer.